Even monkeys can subtract

Humans may not be the only intelligent animals on Earth, for a new study has shown that monkeys can subtract.

Duke University researchers, who conducted the study, said that the discovery marks the first time a nonhuman species has been seen having ‘widespread success’ with subtraction, reports National Geographic News.

In the study, the researchers found that rhesus macaques placed in front of touch screens were able to subtract dots—not by counting them individually but by using a more instantaneous ability researchers call number sense.

Psychologist Jessica Cantlon, who co-led the studies at Duke, said that in the vast majority of trials, the monkeys chose the right answer without counting.

In fact, college students used as controls in the study had the same success rate as the macaques—each group choosing the correct answer in as little as a second, Cantlon said.

Such similarities "suggest that these abilities are part of a primitive system for reasoning about numbers that has been passed down for millions of years of evolutionary time," she said.

Cantlon said that though previous studies have shown a limited capability for subtraction among nonhuman animals, the new data are "the first evidence of widespread success."

She said that previous experiments by other researchers, for example, used only small numbers.

Past studies also did not vary the dot sizes in the multiple choice section, so the larger number always looked physically bigger—possibly tipping off the animals to which set of dots represented the larger sum.

A 2007 study, co-authored by Cantlon, proved monkeys'' success with addition—again on par with college students performing the same tasks.

Cantlon said that animals'' knack for numbers can boost survival in the wild.

For example, research has shown that apes can determine at a glance roughly how much food is present in an area and decide whether to stay and eat or to move on, she said.

The study has been presented at an American Association for the Advancement of Science meeting in Chicago.